The invention relates to a portable workbench including at least two top members supported on a supporting structure. The supporting structure includes a collapsible leg assembly for supporting the top members above a floor surface. One of the top members can be rotated through an angle and moved against the workpiece in a plane defining an angle with respect to the supporting structure to thereby cause the top members and the supporting structure to conjointly define a three point clamping system. Depending on the angular position of the one top member, the portable workbench is suitable for clamping workpieces having various shapes including those of cylindrical or polygonal configuration.
Up to the present time, the general configuration of the workpiece has dictated to the operator which workbench is to be used for clamping the workpiece. For example, workbenches are known wherein a fixed jaw and a movable jaw are both members having a flat and elongated configuration carried on a supporting structure having legs. The movable jaw can be moved away from and toward the fixed jaw by means of threaded spindles actuated manually by means of a crank. The angular adjustment of these jaws is always made in the same horizontal plane conjointly defined by the upper surfaces of the two jaws. The workpiece can then be clamped only between the mutually adjacent vertical clamping surfaces defined by the two jaws.
This is a limitation and frequently prevents an operator from working on the workpiece in its most favorable position and in some cases prevents the operator from working with the vise altogether. Often an operator must do work on a workpiece of cylindrical or some other shape as opposed to workpieces which are of square or rectangular section. For clamping such a workpiece effectively, it is necessary that the workpiece be held at least at three points about its periphery. With regard to tubular conduit for example, the operator would normally reach for a special clamping arrangement having V-shaped grooves in each of its clamping jaws so that the workpiece would be held at four locations about its periphery. Thus, it becomes apparent that the operator would have to have at least two clamping arrangements in order to perform work in most situations. Even at that, however, the operator could not necessarily work on a workpiece in the most desirable position. Often, it is desirable to be able to clamp a workpiece down on a horizontal work surface of a workbench so that operations such as planing or routing can be performed.
Another type of clamping arrangement has been suggested in French Pat. No. 1,287,657 to Travers, wherein a workpiece can be clamped to either of two clamping surfaces of a first clamping jaw of a clamping arrangement having two clamping jaws. The first clamping jaw can be clamped to the top of a table so as to be held in a substantially horizontal plane so that one of its clamping surfaces is in a vertical plane and its other clamping surface is in the horizontal plane. The second clamping jaw has one clamping surface and is pivotally mounted to the first clamping jaw with the aid of two threaded rods and is rotatable between two positions ninety degrees apart. The threaded rods are pivotally mounted in recesses of the first jaw. The French patent teaches that the clamping jaws can be used to clamp a workpiece in either of two positions, namely, when the second jaw is in a first position wherein the clamping surface of the second jaw is in the vertical position and in a second position wherein the clamping surface of the second jaw is horizontal and parallel to the horizontal clamping surface of the first jaw.
Although with this clamping arrangement the operator has the capability of clamping a workpiece to a horizontal work surface, the operator cannot clamp a workpiece of, say, tubular configuration because for each of the two positions, there are only two clamping surfaces. As mentioned, above, to hold a workpiece of tubular configuration effectively requires at least three clamping surfaces. Therefore, even if the operator has a clamping arrangement of the type taught by Travers, the operator would still need an additional vise such as a pipe vise.
Another disadvantage of the clamping arrangement of the type disclosed in the French patent is that long workpieces of rectangular section cannot be effectively held down upon the clamping surfaces of the first clamping jaw since such a workpiece can only be inserted between the clamping surfaces of the two jaws to the depth of the threaded rods which pass through the longitudinal center of the second jaw. When clamping the workpiece, a turning moment is developed which causes the second jaw to slip off of the workpiece.